Analysts and business leaders expressed scepticism and disappointment about Gordon Brown's pre-budget report this evening.

The chancellor admitted UK economic growth was only half what he forecast in March's budget, scaling back his prediction from between 3% and 3.5% to just 1.75%.

But he said the economy would expand by up to 2.5% next year - a figure treated warily by some analysts.

Investec economist David Page said: "We think he has too rosy a view as the eurozone has question marks over it and the global economy could be softer than the Treasury is looking at."

ING economist James Knightley said the new projections were more in line with expectations in the City, but he still considered them to be too optimistic. He said growth may only be 1.8% next year.

"In an environment of rising unemployment, very weak consumer spending and confidence, subdued industrial activity and growing worries about a US-led global slowdown next year, we struggle to find an optimistic spin on the economic outlook," he said.

The chancellor said the economic slowdown was due to rising oil prices and a flat housing market.

As widely expected, he announced an increase of the North Sea oil charge. But this was doubled from 10% to 20% instead of the more modest rise of around 5% predicted by analysts.

The increase could cost BP alone £400m a year if oil prices remain at around $60US a barrel.

"Governments levy taxes and we will do what we have to. But any extra tax that we pay is money that is no longer available for investment in North Sea oil and gas fields," said a BP spokesman.

Julian Small, oil industry taxation expert at Deloitte, said: "Based on our numbers, [the increase] will raise about £1.4bn for the chancellor next year and £5.2bn over the three-year window to 2008."

Environmental groups were disappointed with the pre-budget announcement, saying the chancellor could have done more to tackle carbon emissions from traffic.

"It was the ideal time to introduce a special level of tax on 'gas guzzlers' and on the ultra-cheap flights that are also fuelling emissions. This is a pre-budget report for Top Gear rather than for the long term," said Stephen Joseph, director of Transport 2000.

Mr Brown announced today that 18,500 civil service posts had been cut this year, with 10,000 of them from the Department for Work and Pensions, and 3,500 from Revenue and Customs. The cuts have saved the government a total of £4.7bn.

But his announcement angered trade unions, who accused him of "boasting" about the cuts.

A spokesman for the Public and Commercial Services union said: "Rather than championing crude job cuts, the chancellor should be stepping back and looking at the damage being caused to services which are used by some of the most vulnerable in society."

The chancellor's pre-budget report also announced new tax credits for filmmakers to encourage producers to use UK talent and facilities.

Big budget films will get a credit of 16% and smaller films a tax credit of at least 20%.

The films minister, James Purnell, welcomed the move this afternoon.

"This is good news for the UK film industry. The government has always stated its commitment to supporting and encouraging British film production," he said. "This will allow the UK to remain a prime destination for big and small budget films."

In a bid to create more affordable housing in Britain, Mr Brown announced a new shared equity scheme with mortgage lenders, under which homebuyers would have to find the cash for only 75% of a property's asking price.

The remaining 25% would be split equally between the government and the mortgage lender with whom they had taken out their loan.

The Council of Mortgage Lenders welcomed the announcements on shared equity schemes.

Peter Williams, the deputy director general of the CML, said: "The new private funding for equity loans, although modest in scale, will give us real experience of operating a public/private support scheme for first-time buyers. If it succeeds, it could over time open up a welcome increase in flexible options across the wider housing market."